Near field RF (radio frequency) communication requires an antenna of one near field RF communicator to be present within the alternating magnetic field (H field) generated by the antenna of another near field RF communicator by transmission of an RF signal (for example a 13.56 Mega Hertz signal) to enable the magnetic field (the H field) of the RF signal to be inductively coupled between the communicators. The RF signal may be modulated to enable communication of control and/or other data.
Near field communication in the context of this application may be referred to as near-field RF communication, near field RFID (Radio Frequency Identification) or near field communication. The range of such devices depends on the antenna used but may be, for example, up to 1 meter. A near field RF communicator may be, as examples: an initiator near field RF communicator (such as a near field RFID transceiver or RFID reader) that is capable of initiating a near field RF communication (through transmission or generation of an alternating magnetic field) with another near field RF communicator; a target near field RF communicator (such as an RF transponder or tag) that is capable of responding to initiation of a near field RF communication by another near field RF communicator; or an NFC communicator that is capable of being both an initiator and target and that in an initiator mode is capable of initiating a near field RF communication (through transmission or generation of an alternating magnetic field) with another near field RF communicator and in a target mode is capable of responding to initiation of a near field RF communication by another near field RF communicator.
Communication of data between NFC communicators may be via an active communication mode in which the NFC communicator transmits or generates an alternating magnetic field modulated with the data to be communicated and the receiving NFC communicator responds by transmitting or generating its own modulated magnetic field, or via a passive communication mode in which one NFC communicator transmits or generates an alternating magnetic field and maintains that field and the responding NFC communicator modulates the magnetic field to which it is inductively coupled with the data to be communicated, for example by modulating the load on the inductive coupling (“load modulation”). Near field RF communicators may be actively powered, that is have an internal or associated power source, or passively powered, that is derive a power supply from a received magnetic field. Generally an RF transceiver will be active powered while an RF transponder may be passively or actively powered.
There are several standards in existence which set out certain communication protocols and functional requirements for near field communication. For example ISO/IEC 14443 sets out certain criteria for proximity card and reader/writer systems, ISO 15693 sets out certain criteria for vicinity card and reader/writer systems. Examples of NFC communicators include those described in standards ISO/IEC 18092 and ISO/IEC 21481. NFC communicators may also be referred to as CLFs within standards.
All of these standards require communication to be in accordance with certain timing protocols. For example under the NFC standards ISO/IEC 18092 and ISO/IEC 21481, a responding NFC communicator must supply data in answer to a request within 87 micro seconds (plus or minus 6.5 micro seconds). An NFC communicator may reside within a variety of end systems and host devices, for example mobile telephones, laptops, PDAs. The NFC communicators in such end systems and host devices may be used to transfer data from a variety of sources within those end systems and host devices.